There are numerous substances for which sustained, airborne release of controlled concentration is desirable. Of particular interest worldwide are methods and devices capable of releasing substances that repel insects, particularly biting or disease vectoring species. Some of the most effective substances for repelling insects tend to have a high volatility, which allows them to spread more easily throughout an area making them effective spatial repellents. An unfortunate consequence of this high volatility is that they are short-lived and susceptible to environmental factors such as wind, humidity, and temperature.
There is also some evidence that long-range dispersal caused by saturation of a given area can send confusing signals that indicate the presence of a host and actually attract, rather than repel, insects to the area. (M. Debboun, S. P. Frances, and D. Strickman. 2007. Insect Repellents: Principles, Methods, and Uses. pgs. 13-14, CRC Press, Boca Raton, Fla.). However, some substances are specifically utilized because they have the ability to attract insects. Often, eradication of an insect necessitates that it be attracted to the control or eradication means, whether it be chemical, biological, or mechanical. Some biocontrol substances require contact with, or even ingestion by, an insect. Thus, dispersal mechanisms of a substance that will attract an insect to a specific area are often utilized.
A variety of release mechanisms, including various apparatuses, materials, formulations, and techniques, have been developed to try to provide a sustained, controlled release of volatile substances. Typically, these devices release an initial high concentration, which then tapers off, releasing less of the substance over time. As the amount of substance being released lessens, it can eventually become ineffective, often before the repellent is exhausted. Various binding agents or additives can be added to the repellent to try to slow and control the release and provide longer protection. But these agents and additives dilute the repellent and usually reduce their effectiveness more quickly. Depending upon the release apparatus, the type of substance, repellent or attractant, and environmental factors, an effective amount of the substance can be provided for a few hours and maybe up to a few days before the release mechanism has to be replaced or recharged.
In some situations, it is not possible or feasible to replace or recharge a substance release mechanism regularly or within a short period of time. One example is the use of repellents with livestock. It is well-known that livestock can benefit significantly by reduction of insect annoyance. For livestock farmers and animal breeders, particularly horse and cattle breeders, fighting pests is one of the most expensive and time-consuming issues that they deal with daily. The use of spatial repellents is usually not feasible with roaming livestock. Thus, more common techniques for controlling livestock pests include release mechanisms such as dust bags, impregnated ear tags, repellent misters, or other direct external repellent application to the animal. Pests in animal housing, i.e., barns, stalls, pens, etc., are often controlled with spatial release mechanisms that provide protection within a given area. However, all of these mechanisms exhibit the same disadvantages discussed above, an initial, usually short-term, effectiveness tapering off to an ineffective concentration within a relatively short time period. Needless to say, for a large animal herd, or animals scattered over a large area, repeated applications or recharging of repellent release mechanisms can be tedious and time-consuming.
There is an ongoing need for a release mechanism that can operate with short-lived, volatile insect repellents, attractants, biopesticides, pesticides, or other active ingredients to increase their efficacy and effectiveness over a longer period of time. A release mechanism that can provide an efficient spatial dispersal system with sustained release at optimal levels would be advantageous. Such a release mechanism, could achieve effective levels of protection with less toxic or harsh active ingredients, if such ingredients could be sustained at effective levels. Ideally, such a device would be amenable for use in stationary or mobilized applications, such as, for example, on or around roaming livestock or within their living areas.